QUESTION BANKRADIATION
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QUESTION BANKRADIATION
Number of questions on radiation are given. Finding and
learning their answers will increase both knowledge and
understanding. It is likely to be useful for the examination.
Further, it will also help in the application of the
fundamentals in the design.
2 MARKS QUESTIONS
Explain the followings:

Radiation heat transfer process.

Black body.

Differentiate a grey and a black body.

Monochromatic emissive power.

Emissive power.

Difference between emissivity and absorptivity.

Reflectivity

Radiation shape factor.

Mention Planck’s law of radiation.

Stefan’s Boltzmann law of radiation.

Kirchhoff’s law of radiation.

Wien’s Displacement law of radiation.

Irradiation.

Radiosity.

Radiation shield.

Law of sum mission in shape factor algebra

Law of reciprocity in shape factor algebra

Show that absorptivity of a radiating body is equal to its emissivity.

Main laws of black body radiation.

Definition of view factor and discuss its importance.

Surface resistance.

Space resistance.
5 marks questions

Differentiate between Planck’s law and Stefan’s Boltzmann’s laws of radiation.

Discuss the Differences between absorptivity and reflectivity.

Difference between absorptivity and transmissivity.

State the difference between reflectivity and transmissivity

Derive the relation for the Wien’s displacement law.

Draw and explain Wien’s displacement law.

Do the derivation of the relation for radiation heat transfer between two parallel infinite grey surfaces.

Give and prove the relation for heat reduction equation through a radiation shield.

What is difference between space and surface resistances?
8 MARKS QUESTIONS

Calculate the followings for an industrial furnace in the form of a black body at 2500^{0}
(i) Monochromatic emissive power at 1.2 μm, apply Planck’s Law E_{λ}_{b} = 2.014 x 10^{12} W/m^{2}
(ii) Wavelength at which emission is maximum, using λ_{m}T = 2898, λ_{m} = 1.045 μm

Maximum spectral (monochromatic)emissive power, (E_{λ}_{b})_{max} = 1.285 x 10^{5}T^{5} W/m^{2} per m = 2.1 x 10^{12} W/m^{2} per m

Total emissive power—Use Stefan’s Boltzmann’s Law, E_{b} = σ T^{4} = 3.352 x 10^{6} W/m^{2}

Total emissive power if the furnace is a real body with emissivity as 0.9—Use Stefan’s Boltzmann’s Law for a grey body, E_{gb} = εσ T^{4} = 3.017 x 10^{6} W/m^{2}

The intensity of total radiation, I = E_{b}/= W/m^{2} Co6

Assuming the Sun (dia=1.4 x 10^{9}m) as a black body having a surface temperature of 5750 K and a mean distance of 15 x 10^{10}m from the earth, and earth dia = 12.8 x 10^{6}m. Calculate the followings:
(i) Total energy emitted by the sun=q^{.}=E_{b} A = E_{b} x r ^{2}_{sun} = 3.816 x 10^{26 }W
(ii) Emission received per m^{2} just outside the atmosphere of the earth, given distance, d = 1.5 x 10^{10}m, area 4d^{2} ,
Emission received = 3.816 x 10^{26}/4 d^{2} =3.816 x 10^{26}/4 (1.5 x 10^{10})^{2}= 1349.6 W/m^{2} = Solar constant
(iii) Total energy received by the earth= Solar constant x projected area of earth = 1349.6 x r^{2}_{earth}=1.736 x 10^{17} W
(iv) Monochromatic emissive power at 1.2 μm, apply Planck’s Law
(v) Wavelength at which emission is maximum, using λ_{m}T = 2898, λ_{m}

Maximum spectral (monochromatic)emissive power, (E_{λ}_{b})_{max} = 1.285 x 10^{5}T^{5} W/m^{2} per m

Total emissive power if the furnace is a real body with emissivity as 0.9—Use Stefan’s Boltzmann’s Law for a grey body, E_{gb} = εσ T^{4} =

The intensity of total radiation, I = E_{b}/= W/m^{2} Co6

The filament of a 75 W light bulb may be considered as a black body radiating into a black enclosure at 70^{0} The filament diameter is 0.10 mm and the length is 5 cm. considering the radiation, determine the filament temperature. (2756^{0}C), Co6

Determine the rate of heat loss by radiation from a steel tube of outside diameter 70 mm and 3 m long at a temperature of 227^{0} If the tube is enclosed in a square brick conduit of 0.3 m side and is at 27^{0}C. Take ε_{steel}0.79 and b_{rick}=0.93. (1589.7 W), Co6

A long cylindrical heater 25 mm diameter is maintained at 660^{0}C and has a surface resistivity of 0.8. The heater is located in a large room whose walls are at 27^{0} How much will the radiant heat transfer from the heater is reduced if it is surrounded by a 300 mm diameter radiation shield of aluminum having an emissivity of 0.2? What is the temperature of the shield? (37.45 % & 364^{0}C), Co6

For a hemispherical surface, the flat floor is at 700 K and has an emissivity of 0.5. The hemispherical roof is at 1000^{0}C and has an emissivity of 0.25. Find the net radiative heat transfer from t5he roof to the floor. (12310.4 W/m^{2}), Co6

The two large parallel planes with emissivity’s 0.3 and 0.8 exchange heat. Find the percentage reduction when a polished aluminum shield of emissivity of 0.04 is placed between them. Use the method of electrical analogy. (93.2 %), Co6